bpf: Add BTF_ID_LIST/BTF_ID/BTF_ID_UNUSED macros

Adding support to generate .BTF_ids section that will hold BTF
ID lists for verifier.

Adding macros that will help to define lists of BTF ID values
placed in .BTF_ids section. They are initially filled with zeros
(during compilation) and resolved later during the linking phase
by resolve_btfids tool.

Following defines list of one BTF ID value:

  BTF_ID_LIST(bpf_skb_output_btf_ids)
  BTF_ID(struct, sk_buff)

It also defines following variable to access the list:

  extern u32 bpf_skb_output_btf_ids[];

The BTF_ID_UNUSED macro defines 4 zero bytes. It's used when we
want to define 'unused' entry in BTF_ID_LIST, like:

  BTF_ID_LIST(bpf_skb_output_btf_ids)
  BTF_ID(struct, sk_buff)
  BTF_ID_UNUSED
  BTF_ID(struct, task_struct)

Suggested-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-4-jolsa@kernel.org

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index db600ef..0be2ee2 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -641,6 +641,10 @@
                __start_BTF = .;                                        \
                *(.BTF)                                                 \
                __stop_BTF = .;                                         \
+       }                                                               \
+       . = ALIGN(4);                                                   \
+       .BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) {                   \
+               *(.BTF_ids)                                             \
        }
 #else
 #define BTF

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
new file mode 100644 (file)
index 0000000..fe01977
--- /dev/null
+++ b/include/linux/btf_ids.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_BTF_IDS_H
+#define _LINUX_BTF_IDS_H
+
+#include <linux/compiler.h> /* for __PASTE */
+
+/*
+ * Following macros help to define lists of BTF IDs placed
+ * in .BTF_ids section. They are initially filled with zeros
+ * (during compilation) and resolved later during the
+ * linking phase by resolve_btfids tool.
+ *
+ * Any change in list layout must be reflected in resolve_btfids
+ * tool logic.
+ */
+
+#define BTF_IDS_SECTION ".BTF_ids"
+
+#define ____BTF_ID(symbol)                             \
+asm(                                                   \
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"     \
+".local " #symbol " ;                          \n"     \
+".type  " #symbol ", @object;                  \n"     \
+".size  " #symbol ", 4;                        \n"     \
+#symbol ":                                     \n"     \
+".zero 4                                       \n"     \
+".popsection;                                  \n");
+
+#define __BTF_ID(symbol) \
+       ____BTF_ID(symbol)
+
+#define __ID(prefix) \
+       __PASTE(prefix, __COUNTER__)
+
+/*
+ * The BTF_ID defines unique symbol for each ID pointing
+ * to 4 zero bytes.
+ */
+#define BTF_ID(prefix, name) \
+       __BTF_ID(__ID(__BTF_ID__##prefix##__##name##__))
+
+/*
+ * The BTF_ID_LIST macro defines pure (unsorted) list
+ * of BTF IDs, with following layout:
+ *
+ * BTF_ID_LIST(list1)
+ * BTF_ID(type1, name1)
+ * BTF_ID(type2, name2)
+ *
+ * list1:
+ * __BTF_ID__type1__name1__1:
+ * .zero 4
+ * __BTF_ID__type2__name2__2:
+ * .zero 4
+ *
+ */
+#define __BTF_ID_LIST(name)                            \
+asm(                                                   \
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"     \
+".local " #name ";                             \n"     \
+#name ":;                                      \n"     \
+".popsection;                                  \n");   \
+
+#define BTF_ID_LIST(name)                              \
+__BTF_ID_LIST(name)                                    \
+extern u32 name[];
+
+/*
+ * The BTF_ID_UNUSED macro defines 4 zero bytes.
+ * It's used when we want to define 'unused' entry
+ * in BTF_ID_LIST, like:
+ *
+ *   BTF_ID_LIST(bpf_skb_output_btf_ids)
+ *   BTF_ID(struct, sk_buff)
+ *   BTF_ID_UNUSED
+ *   BTF_ID(struct, task_struct)
+ */
+
+#define BTF_ID_UNUSED                                  \
+asm(                                                   \
+".pushsection " BTF_IDS_SECTION ",\"a\";       \n"     \
+".zero 4                                       \n"     \
+".popsection;                                  \n");
+
+
+#endif